1. Technical Field of the Invention
The present invention relates to a wiring board, a process for producing the same, a display device, and an electronic device.
2. Conventional Art
In recent years, portable electronic devices such as mobile phones have rapidly become widespread. Electronic devices generally have a wiring board (printed board) having various kinds of IC chips mounted thereon.
There is a strong demand for reducing the weight of portable electronic devices. Various techniques for satisfying these demands have been proposed for various components forming the electronic devices. This also includes the wiring board, and techniques for satisfying the demands for reduced weight are being developed. On the other hand, electronic devices having high performance are also demanded, and therefore it can be said that there are strong demands for developing a technique realizing weight reduction without impairing performance.
The invention has been achieved in view of these circumstances, and an object thereof is to provide a wiring board that can realize weight reduction and a process for producing the same, as well as a display device and an electronic device using the wiring board.
In order to solve the problems, the wiring board of the invention comprises a base member having a mounting region on which an integrated circuit having a plurality of terminals is mounted, a plurality of wiring lines formed on the base member are connected to the plurality of terminals of the integrated circuit, and a conductor pattern is formed on the mounting region of the base member and is connected to the plurality of wiring lines, and is characterized in that the conductor pattern is maintained at a prescribed potential and has a shape extending in a substantially radial form toward the plurality of wiring lines.
According to the wiring board, the conductor pattern for interconnecting the plurality of wiring lines to be grounded has a shape extending in a radial form inside the mounting region. Therefore, the conductor pattern can be formed with a small amount of material as compared to the case of a conductor pattern covering most of the mounting region (a so-called xe2x80x9csolid patternxe2x80x9d), thereby realizing a reduction in weight of the wiring board.
Furthermore, because the conductor pattern is maintained at the prescribed potential, electrical noise generated from the integrated circuit and electrical noise carried from the outside can be attenuated. Therefore, an effect in that the influence of the electrical noise to the components forming the electronic equipment is decreased can also be obtained.
In the case where a conductor pattern is formed to cover most of the mounting region, a problem arises in that the wiring lines and the conductor pattern, which essentially should not be short circuited, are liable to be electrically shorted because the distance between the conductor pattern and the wiring lines becomes small. On the other hand, the conductor pattern of the wiring board according to the invention has a shape extending in a radial form with respect to the wiring lines to be grounded with the prescribed point as the center. Therefore, a distance that is sufficient to prevent short circuiting between the wiring lines not to be grounded and the conductor pattern can be ensured.
In view of the standpoint where the conductor pattern has the shape extending in a substantially radial form from the prescribed point in the mounting region, it is preferred that the prescribed point is positioned in the vicinity of the center of the mounting region. According to this arrangement, in the case where, for example, a structure wherein the plurality of wiring lines are arranged along the outer periphery of the mounting region of a substantial quadrangular shape is employed, a sufficient distance can be ensured between the wiring lines not to be grounded and the conductor pattern, and therefore, short circuiting formed thereby can be more certainly prevented. In the case where the mounting region has a rectangular shape, the plurality of wiring lines may contain one or more wiring lines formed to cut across one side of the mounting region and one or more wirings lines formed to cut across another side adjacent to the one side.
It is also preferred that the integrated circuit is mounted on the mounting region of the base member through an anisotropic conductive film having conductive particles dispersed therein. According to this arrangement, the terminals of the integrated circuit and the wiring lines on the substrate can be connected at the same time as connecting the integrated circuit to the base member, whereby the production process can be simplified, and the production cost can be reduced.
In the case where the integrated circuit is mounted by using the anisotropic conductive film, it is preferred that the mounting region has an area of a region having the conductor pattern formed thereon that is smaller than an area of a region other than that region. According to this arrangement, the region on the mounting region having no conductor pattern formed, i.e., the region with the surface of the base member exposed, can be assured to be relatively wide, and therefore, the following effects can be obtained. That is, in the case where, for example, a conductor pattern formed with a copper thin film having gold plating is formed on a base member formed of polyimide, the adhesion strength to the anisotropic conductive film at the surface of the base member is generally higher than that at the surface of the conductor pattern. Therefore, a conductor pattern of the substantially radial form is employed to form a large area in the mounting region where the base member is exposed, whereby the adhesion strength between the base member and the integrated circuit can be improved.
When a member in a thin plate form that is permeable to moisture is used as the base member, an effect can be obtained in that moisture contained in the anisotropic conductive film can be released to the outside through the base member. When the area in the mounting region with the surface of the base member exposed is ensured to be large, the region that is permeable to moisture can be made larger, and the effect can be more remarkably exhibited.
It is also preferred that a material having flexibility is used as the base member. According to this arrangement, in the case where, for example, the wiring board is used as a display panel, a structure wherein the wiring board can be folded to the back side of the display panel can be employed, and thus miniaturization of the electronic device can be accomplished. The wiring board according to the invention may also have a structure wherein it has a substrate having a mounting region on which an integrated circuit is mounted, and a conductor pattern which is formed on the mounting region and which is grounded, and wherein the conductor pattern has a shape extending in a substantially radial form from a prescribed point in the vicinity of a center of the mounting region.
Furthermore, in order to solve the problems, the invention relates to a display device comprising a display panel having an electro-optical substance held between a first electrode and a second electrode facing each other, and characterized by comprising a base member connected to the display panel, an integrated circuit which has a plurality of terminals and which is mounted on the base member, a plurality of wiring lines formed on the base member, which are connected to the plurality of terminals of the integrated circuit, and a conductor pattern which is formed on the mounting region of the base member on which the integrated circuit is mounted and which is connected to the plurality of wiring lines, wherein the conductor pattern is maintained at a prescribed potential and has a shape extending in a substantially radial form toward the plurality of wiring lines.
As the display panel, a liquid crystal panel containing a liquid crystal may be used as the electro-optical substance, or alternatively, an EL panel using an EL (electro-luminescence) luminescence layer may be used as the electro-optical substance. As the integrated circuit to be mounted on the base member, one having a circuit for generating a voltage to be applied to at least one of the first electrode and the second electrode may be used. Furthermore, the invention can also be practiced in an embodiment of an electronic device using the display device as a display part.
In order to solve the problems, the invention relates to a method for producing a wiring board comprising a base member having an integrated circuit mounted thereon and a plurality of wiring lines which are formed on the base member and which are connected to a plurality of terminals of the integrated circuit, characterized by comprising a step of forming a conductor pattern having a shape extending in a substantially radial form toward the plurality of wiring lines on a mounting region of the base member on which the integrated circuit is mounted, and a step of mounting the integrated circuit on the mounting region. According to a circuit board obtained by this method, the effects similar to the foregoing wiring boards can be obtained.
When this production method is used, it is preferred that the integrated circuit is connected to the base member via an adhesive having conductive particles dispersed therein upon mounting the integrated circuit. More specifically, it is preferred that the integrated circuit is pressed on the base member in a state where the adhesive intervenes between the integrated circuit and the base member. By doing so, the terminals of the integrated circuit and the wiring lines on the base member can be connected at the same time as connecting the integrated circuit to the base member, thereby simplifying the production process, and allowing the production cost to be reduced.